1. Field of the Invention
This invention relates to improved feedstuffs and/or water for poultry and methods for their use. More specifically, this invention relates to a poultry feed or water additive and dietary changes which alleviate respiratory alkalosis and associated increased mortality, decreased egg shell thickness and decreased growth rate that occur during periods of severe heat stress.
2. Description of the Prior Art
It is generally known that poultry such as chickens, geese, turkeys, quail, pheasants and the like are particularly susceptible to poor productivity (reduced growth rate, feed efficiency, egg shell quality and high mortality) during periods of environmental heat stress (high temperatures and high relative humidity). Controversey exists in contemporary scientific literature regarding the occurrence of alkalosis in heat stressed birds and consequently, no therapeutic treatment for alkalosis founded or based on direct scientific evidence is available and to the best knowledge of the inventor, no direct knowledge of a poultry bicarbonate ion requirement during heat stress existed prior to the present invention.
It is known that heat stress substantially reduces the growth rate of broiler chicks. Diets have been altered to reduce this problem via reducing the heat increment of the diet with fat supplementation (H. L. Fuller et al; "Effect of Heat Increment of the Diet on Feed Intake and Growth of Chicks Under Heat Stress", Proc. Maryland Nutr. Conf., pp 58-64, 1973) and improved the amino acid balance (P. W. Waldroup et al; "Performance of Chicks Fed Diets Formulated to Minimize Excess Levels of Essential Amino Acids", Poultry Sci., 55:243-253, 1976). It has also been suggested that the decline in growth rate results directly from reduced feed intake (R. L. Squibb et al; "Growth and Blood Constituents of Immature New Hampshire Fowl Exposed to Constant Temperatures of 99.degree. for 7 Days", Poultry Sci., 38:220-221, 1959). It has been demonstrated that the growth rate of heat stressed broilers can be increased by force feeding at a level exceeding ad libitum feed intake (M. O. Smith et al; "Feed Intake and Environmental Temperature Effects Upon Growth, Carcass Traits, Ration Digestibility, Digestive, Passage Rate and Plasma Parameters in Ad Libitum and Force-Fed Broiler Chicks" Poultry Sci., 62: 1504 abstr., 1983). It is also generally known that blood alkalosis precipitated through altering the Na/Cl ratio (S. Hurwitz et al; "Sodium and Chloride Requirements of Chick; Relationship to Acid-Base Balance", Poultry Sci., 52:903-909, 1773) reduces both the feed consumption and growth rate of chicks; however, the studies were not thermal stress, per se.
At high ambient temperatures, evaporative cooling through panting is an important means of heat loss for fowl (G. M. Jukes, "Transport of Blood Gases", In: Physiology and Biochemistry of the Domestic Fowl, Vol. 1 Bell and Freeman, eds., Academic Press, N.Y., 1971). Hyperthermic panting has precipitated respiratory alkalosis (S. A. Richards; "Physiology of Thermal Panting in Birds", Ann. Biol. Anim. Biophys., 10:151-168, 1970). However, respiratory alkalosis has not been consistently observed in fowl exposed to thermal stress. Parker et al ("Thermal Stress Effects on Certain Blood Characteristics of Adult Male Turkeys", Poultry Sci. 50:1287-1295, 1971) observed that the pH in the male turkey decreased when exposed to thermal stress, while Kohne et al ("Changes in Plasma Electrolyetes, Acid-Base Balance and Other Physiological Parameters of Adult Female Turkeys Under Conditions of Acute Hyperthermia", Poultry Sci., 54:2034-2038, 1975) reported that acute hyperthermia produced profound alkalosis, but chronic hyperthermia ("Acid-Base Balance, Plasma Electrolytes and Production Performance of Adult Turkey Hens Under Conditions of Increasing Ambient Temperature", Poultry Sci., 54:2038-2045, 1975) has no effect. Darre et al ("Time Course of Change in Respiratory Rate, Blood pH and Blood pCO.sub.2 of SCWL Hens During Heat Stress", Poultry Sci., 59:1598 abstr., 1980) observed that pH increased in a curvilinear fashion as leghorn hens were exposed to increasing ambient temperature changes. Siegel et al ("Blood Parameters of Broilers Grown in Plastic Coops and on Litter at Two Temperatures", Poultry Sci., 53:1016-1024, 1974) found no difference in blood pH for broilers reared under continuous 35.degree. C. versus thermoneutral conditions. This result agreed with Vo et al ("The Effect of High Temperatures on Broiler Growth", Poultry Sci., 54:1347-1348 abstr. 1975), but contradicted the work of Bottje et al ("Effect of an Acute Heat Stress on Blood Flow in the Coeliac Artery of Hubbard Cockerels", Poultry Sci., 62:1386-1387 abstr., 1983) wherein it was reported that blood pH was elevated. And, Parker et al ("Effect of Thermal Stress on Adult Male Turkeys", Poultry Sci., 49:1425 abstr, 1970) reported that heat stress had no effect on blood pH other than the fact that pH was more variable among heat stressed birds than thermoneutral controls. Although the reasons for these discrepancies are not clear, they may include the degree of thermal stress, type of stress (acute versus chronic), blood collection site or the like and in view of the teachings of the present invention may involve the sampling time relative to the respiratory state of the birds. According to the present invention, it is observed that the birds exposed to chronic thermal stress exhibit a respiratory cycle of panting and non-panting phases which result in an oscillation between normal and alkalotic blood conditions.